Present warmer drawers use multiple/infinite function mechanical controls to control and maintain the food temperatures. These mechanical controls provide many options for setting temperatures for holding and warming food. Temperatures can range from ambient (temperature outside the appliance) to 230 degrees Fahrenheit (F.) and any temperature in between. These multiple/infinite function mechanical controls are inaccurate and have a tendency to dry food out, overheat, have large swings in temperature ranges from set point, which results in over and undershoots. This is partly due to the fact that users set the wrong temperature for holding or warming. These mechanical controls when placed in a warmer drawer do not show the precise temperature number or set point. The interface graphics merely show proof, low, medium or high. Other units may show a number at a location when in fact the user does not know what the inside temperature is without using some other means.
The sensors used to detect the present temperature in the chamber are mostly capillary tubes using expanding gases, liquids, and force transferring to a mechanical snap action switch, causing the switch to close or open. Thus supplying current to, or turning off, current to a heater, such as a cal rod. The response time for these types of controls is slow with the results of the heating of the chamber having overshoots and undershoots in temperature. With the user having the ability to set an infinite number of temperature set points, setting the right temperature can be a problem for the user. If the user sets the temperature too low for the food, the inside cavity chamber cools the food down. The user makes corrections to the temperature setting by increasing the setting to a new set point to which the resulting controller change results in a long lag for the cavity chamber to reach and become stable. This lag in time to reach temperature may result in the user setting to a higher set point. The user may continually change set points because of not being able to reach proper temperature. Such procedure can result in frustration and dislike for the warmer drawer as a result of dried out food, overheated or under heated food.
Present warmer drawers and the sensors used within the standard design of operation causes slow response for temperature corrections, thus causing temperatures to greatly overshoot and undershoot. The resulting temperature ranges and swings with multiple function controls, from the on to off cycling, have a greater tendency to drive moisture out of foods, hold more moisture in the chamber, and overcook food(s). Set points for proofing temperatures are typically provided but most users do not make bread in warmer drawers and do not use this feature. The ability of the user to go to lower temperature and higher temperature points and points in between is rarely used. For the most part user can benefit from a factory preset that is between 160 and 200 degrees F.
Present designs for the heating elements are located on the inside of the drawer enclosure. Located at the bottom of the chamber, with a cal rod used in varying patterns, the rod provides radiant heat. The heat produced rises slowly warming from the bottom to the top. Present designs provide varying temperature levels within the chamber. These differing temperatures cause problems for controlling and maintaining the food temperatures. Start up times to get warm temperatures in the cavity can be long due in part to the cal rod design. These long start(s) up times prevent a user from just turning on and placing food in. Present warmer drawers must have pre-heat up times in order to stabilize the temperature inside the cavity. Also as the temperature and heat are cycled you get large overshoots and undershoots of temperature causing food to dry out faster and with the loss of temperature control for longer periods, poor food holding capability results.
Present designs use mechanical switches for setting the desired temperature. These mechanical switches are inaccurate in their setting and repeatability. They have problems maintaining a set point showing swings in temperature partly due to the design of the warmer drawer and method of heating, but also due to the inaccuracy of the mechanical switches itself. Mechanical control switches have a known issue suffering from hysteresis, which contributes to their inaccuracies in the controllability to obtain and hold a set temperature point or repeat a function. This can be seen if you turn the control switch to the right and stop at a setpoint or turning the same mechanical switch going past the set point and then turning the control to the left stopping at the set point. The result will be a difference in temperature at the same set point. This issue results in a user not being able to obtain the same setpoint every time. If accurate, repeatable temperature(s) control is needed then the use of mechanical control does not deliver. The inaccuracy of the mechanical switch contributes to the large temperature swings inside the chamber of the warmer drawer. This inaccuracy contributes greatly to the radiant temperature problems found in most present warmer drawers with the chamber having overshoot and undershoot problems. Present design mechanical switches thus do not provide the user the ability to come back to present location or temperature(s) when setting up the operation for one operation to the next. The user cannot one day set the proper temperature and then the next day return to that same set point if the controls were moved. Temperature swings as much as 30 degrees or more have been seen.
Present designs are for built-in (used in a cabinet by itself) or built in a cabinet under or over a product such as a cook top, oven, or some other appliance. The warmer drawer can be used in a location all by itself, but in all cases are built into a cabinet or some structural frame, which is not moveable. This limits the warmer drawer from being placed in other areas. This also limits the warmer drawer(s) from being used as a freestanding unit, as in a mobile unit, used under a cabinet, or in areas that do not have a structural frame.
Therefore, there exists a need for a single preset temperature warmer drawer in which accurate heating control of food is accomplished. There exists the need for a fixed method of controlling the operation and setting of temperature in a warmer drawer. There is a further need to accurately apply and control heat to the warmer drawer. There also is a need for a factory preset temperature warning appliance that is portable and can be used outdoors.